The present invention relates to a noble metal-free, solid catalyst composition, its preparation, its use for producing hydrogen peroxide and its use in the epoxidation of olefins.
1. Field of the Invention
Hydrogen peroxide is nowadays widely used as a clean oxidant, for example for the bleaching of paper and cellulose, for the removal of SO.sub.2 from waste gases, in the electronics industry in semiconductor manufacture, and for sterilization, for example deodorization or disinfection of packing material. In organic chemistry, hydrogen peroxide is used particularly in epoxidation and hydroxylation reactions, where hydrogen peroxide can also be generated in situ.
2. Discussion of the Background
According to the prior art, hydrogen peroxide is nowadays prepared largely by the anthraquinone process (cf. Ullmann's Encyclopedia of Industrial Chemistry, 5th edition, vol. A13, pp. 443 ff). The substep of hydrogenation is here usually carried out in the presence of a metal catalyst such as palladium black or Raney nickel. In addition, heterogeneously catalyzed preparative processes in which noble metals on various supports are used as catalyst have been described. Thus, in U.S. Pat. No. 5,320,821, Pd/heteropolyacid is used as catalyst to prepare hydrogen peroxide from the elements. Furthermore, JP 5017106-A discloses the use of silica or zeolites together with platinum metals and EP 0 537 836 discloses the use of zirconium oxides together with Pd.
However, these processes often require the use of halogen compounds as promoters and stabilizers, as described, for example, in U.S. Pat. No. 5,320,821.
In organic oxidation reactions, it is possible to use hydrogen peroxide formed catalytically in situ directly or in combination with peroxo-oxygen transferers (cf. G. Goor in G. Strukul, "Catalytic Oxidations with Hydrogen Peroxide as Oxidant", pp. 13-43, 1992 Kluwer Academic Publishers). In particular, known heterogeneous oxidation catalysts are titanium-containing zeolites whose preparation is described, for example, in DE 3047798. Zeolites of this type are used to transfer oxygen to monoolefins and diolefins (cf. EP 0 100 119 and EP 0 190 609). Compared with the industrial oxidation by the chlorohydrin process (cf. K. Weissermel, H.-J. Arpe, "Industrielle Organische Chemie", 3rd edition, VCH Verlag (1998) pp. 284-289), the process according to EP 0 100 119 has the advantage of making, for example, propylene oxide obtainable in high selectivity from propene. In J. Chem. Soc. Chem. Commun. (1992) 1446-7), Tatsumi describes the hydroxylation of benzene and the oxidation of hexane using hydrogen/oxygen over metallic palladium on TS-1 silicalite, but only low reaction rates compared with hydrogen peroxide are observed.
In addition, DE-A 44 25 672 discloses improved noble metal catalysts containing titanium zeolites and processes for preparing propylene oxide from hydrogen, oxygen and propene. The catalyst systems described therein are very satisfactory, for example, in terms of reactivity, selectivity and stability. However, they nevertheless have the disadvantage, like other heterogeneous oxidation catalysts known from the prior art, of containing an expensive noble metal as catalytically active constituent. This is a significant economic disadvantage, particularly for the large-scale industrial production of the oxidation products such as propylene oxide.